v1.3.4: Fix inflated performance stats from abandoned quizzes

Fixes

• Orphaned quiz results inflating stats — Domain quiz results were recorded to the database as each question was answered. If a quiz was abandoned mid-way (page refresh, navigation, starting a new quiz), those results remained in the database permanently, inflating performance stats without appearing in quiz history. Results are now deferred to submission time, matching the existing exam flow.
• "Quizzes Taken" counter included exams — The overview card counted all sessions instead of filtering to domain quizzes only. Exams already had their own dedicated counter.

New

• Orphan cleanup endpoint — POST /pcip-prep/v1/cleanup-orphaned deletes any pre-existing orphaned result rows from before this fix.

Full Changelog: v1.3.3...v1.3.4